Bottom portion of clip is shifted to left

[nick1977]

Hi all

I have managed to capture a VHS clip that had macrovision, and generally after a bit of filtering in Avisynth and Virtualdub I'm pretty happy with it.
There is however one issue I am not sure how to deal with.
For some reason the bottom 50 or so lines seem to be shifted to the left, leaving a black rectangle on the right.
I've included a screenshot which is before I have applied any filters.


[Attachment 52800 - Click to enlarge]

I know there is the usual VHS noise at the bottom, but this sits above that.
Not sure if the macrovision was the cause or not.
What I need to do sounds simple on paper, but I'm guessing is a little more complicated in reality.
Is there an Avisynth filter or string of commands that will take x number of lines from the bottom, and shift them x number of pixels to the left/right?
I have a basic grasp of Avisynth, but not an expert by any stretch!

Any help gratefully accepted.

[poisondeathray]

You can use crop a bottom version, then overlay it back onto the original using x= coordinates to shift it left or right, y=coordinates to shift it up or down

orig=ImageSource("atex.jpg")
bottom=orig.crop(0,542,0,0,true)
overlay(orig, bottom, x=4,y=542)

[Attachment 52806 - Click to enlarge]

If video is interlaced VHS YUV as 4:2:0 - because it's 542 vertical pixels (mod2, not mod4), you have to do the crop as 4:2:2 . You would need to use ConvertToYV16(interlaced=true) before cropping if it's not already 4:2:2 . Basically, there are rules to cropping, depending on chroma subsampling, and if it's interlaced or not
http://avisynth.nl/index.php/Crop#Crop_restrictions

[nick1977]

Thanks for the quick reply.
I pretty much get the jist of the code, only I'm unsure why it would reference the atex.jpg example still I have provided?
It needs to take the current frame each time and apply the correction, rather than using a static example.
Sorry if I'm misunderstanding, and I could just drop the code is "as is" and then fine tune the figures!

[nick1977]

Don't worry I've worked it out, thanks!

For the benefit of other novices like me, I removed the removed the 'orig=ImageSource("atex.jpg")' line and added the 'orig=' to the beginning of the avisource line in my script.
Works perfectly now.

[poisondeathray]

Thanks for the quick reply.
I pretty much get the jist of the code, only I'm unsure why it would reference the atex.jpg example still I have provided?
It needs to take the current frame each time and apply the correction, rather than using a static example.
Sorry if I'm misunderstanding, and I could just drop the code is "as is" and then fine tune the figures!

You would substitute a different source filter referencing your video, instead of the image . If you had "video.avi", you would use something like this

e.g

orig=AVISource("video.avi")
bottom=orig.crop(0,542,0,0,true)
overlay(orig, bottom, x=4,y=542)

Does the bottom change in terms of how much it moves ? Or is it static in terms of position relative to the top section? Those values in the script are applied on every frame; the overlay is shifted right 4 pixels on every frame . If you needed, say, 6 pixels on some sections, you'd have to divide up the video, or specify sections to apply different settings in the script

[Sharc]

Basically, there are rules to cropping, depending on chroma subsampling, and if it's interlaced or not
http://avisynth.nl/index.php/Crop#Crop_restrictions

Do the cropped picture size or the cropping values have to fulfill the mod rules?

Example:
For YV12 interlaced 720x480i, vertical cropping
a) crop(0,2,0,-2) => 720x476 cropped picture is mod4 compliant, crop values mod 2
b) crop(0,0,0,-4) => 720x476 cropped picture and crop value are mod 4 compliant

Are both ok, or b) only?

[poisondeathray]

Basically, there are rules to cropping, depending on chroma subsampling, and if it's interlaced or not
http://avisynth.nl/index.php/Crop#Crop_restrictions

Do the cropped picture size or the cropping values have to fulfill the mod rules?

Example:
For YV12 interlaced 720x480i, vertical cropping
a) crop(0,2,0,-2) => 720x476 cropped picture is mod4 compliant, crop values mod 2
b) crop(0,0,0,-4) => 720x476 cropped picture and crop value are mod 4 compliant

Are both ok, or b) only?

Only "b" ; It's because of the chroma subsampling in terms of fields

If you perform "a" , you will get messed up chroma ghosting artifacts

[Sharc]

Basically, there are rules to cropping, depending on chroma subsampling, and if it's interlaced or not
http://avisynth.nl/index.php/Crop#Crop_restrictions

Do the cropped picture size or the cropping values have to fulfill the mod rules?

Example:
For YV12 interlaced 720x480i, vertical cropping
a) crop(0,2,0,-2) => 720x476 cropped picture is mod4 compliant, crop values mod 2
b) crop(0,0,0,-4) => 720x476 cropped picture and crop value are mod 4 compliant

Are both ok, or b) only?

Only "b" ; It's because of the chroma subsampling in terms of fields

If you perform "a" , you will get messed up chroma ghosting artifacts

Thanks. This confirms my experience. It's just a bit misleading how it is described in the wikis and tutorials, when one simply refers to 'width' and 'height'.

[Brad]

Weird. At the bottom of your screenshot I see the skewed line (head switch point), then skew-corrected "head-switching noise", then part of the Vertical Sync of the next frame. This means your capture is vertically-delayed; the top of the frame is getting cropped off.

What was your workflow??

[nick1977]

The work flow was:

Panasonic HD640 VCR - Scart connect to Panasonic DMR-ES10 DVD Recorder - composite out to Hauppauge HD-PVR2 Gaming edition.

Three points

1) I am not sure the DVD recorder was doing anything, but I have heard it stabilises the image even if not recording it.
2) I didn't record directly to DVD, as the tape I am trying to record displayed a "cannot record" message - presumably macrovision protected.
3) I wouldn't be surprised if the HD-PVR2 is the culprit, as it does seem somewhat buggy!